text: For Mnemiopsis leidyi, the ability to produce light is first observed upon the development of the plate cilia cells, and the bioluminescent cells found in the embryo share many characteristics with the photocytes observed in the adult organism. The M macromere lineage of cells are the ones that differentiate into photocytes, and they separate from other lineages of cells in the differential division. The subsequent maturation of the photocytes and intensification of light produced develop rapidly, occurring within ten hours of the first observed instance of bioluminescence. The egg of the organism contains two cytoplasmic regions: cortical and yolky, and the region of cytoplasm that daughter cells receive when the egg divides determine what they differentiate into. It was found that whether cortical cells exhibited bioluminescence or not was dependent on whether they inherited yolk in their cytoplasm with the cells containing yolk producing light and the cells without yolk not producing any light.